High-risk neuroblastoma is an aggressive, poorly differentiated tumor often associated with amplification of the MYCN oncogene. However, some high-risk neuroblastomas lack MYCN amplification, suggesting that mechanisms besides MYCN amplification suppress differentiation. We have demonstrated that heparan sulfate proteoglycans (HSPGs), including the type III TGF? receptor (T?RIII), can promote FGF2-induced neuroblast differentiation via enhanced Erk signaling. T?RIII is repressed by N-Myc and this repression is relieved by histone deacetylase (HDAC) inhibition. Several targeted agents in clinical trials function by relieving epigenetic repression, often by inhibiting the actions of N-Mc; however, their effects on differentiation and specific mechanisms of action remain unclear. In preliminary studies, we demonstrate that N-myc-mediates suppression of the HSPGs glypican 1 and syndecan 3, and the HSPG ligand, heparin-binding epidermal growth factor (HBEGF). This suppression is also relieved by HDAC inhibition. We further demonstrate that HDAC inhibitors and other epigenetic-targeted therapies, including inhibitors of aurora kinase A (AurkA) and DNA methyltransferases (DNMT), promote neuroblast differentiation in MYCN-amplified and non-amplified models, while enhancing heparan sulfate signaling. Based on these preliminary studies, we hypothesize that epigenetic mechanisms repress expression of pro-differentiation receptors and ligands. Existing targeted therapies relieve this suppression to promote heparan sulfate signaling and neuroblast differentiation, leading to decreased tumor growth and metastasis. This hypothesis will be addressed by three specific aims. Aim 1: The ability of epigenetic-targeted therapies to promote neuroblast differentiation and suppress proliferation will be examined, including determining which neuroblastoma disease subtypes are susceptible. Aim 2: The mechanism by which epigenetic-targeted therapies promote neuroblast differentiation and suppress proliferation will be examined to determine whether enhanced heparan sulfate signaling is involved. Aim 3: Epigenetic-targeted therapies in combination with ODSH will be utilized to determine whether these therapies act synergistically to enhance heparan sulfate signaling and decrease tumor growth and metastasis in vivo. These studies will determine the epigenetic mechanisms by which a pro-differentiation repertoire is suppressed, identify susceptible disease subtypes that may benefit from these clinically useful treatments, and inform the use of combinatorial therapies for high-risk, chemotherapy-resistant disease.